Metropolitan area networks are typically multi-layer networks comprising a variety of different technologies and protocols. For example, the local loop, which connects an end-user to the local carrier's end office or central office (CO), may be twisted copper pair, coaxial cable, wireless, and in some cases, fiber cable. The service provided to end-users over these loops typically includes telephony, Internet access, and video. However, the communications industry is rapidly changing and service providers are looking towards new services such as high-speed Internet access, high speed data network access (virtual private networks-VPN), high-definition television (HDTV), and interactive Internet gaming, among other high bandwidth services, to provide new revenue streams.
Much of this traffic is sourced from, or destined to, locations outside of the Metropolitan area requiring access to a long haul network, while other traffic is confined within the metropolitan area. Between the point of presence (POP) to the long haul network and the local loop there are a variety of metropolitan access infrastructures and network configurations. However most access infrastructures typically involve central offices connected via a hierarchy of SONET rings. Asynchronous transfer mode (ATM) permanent virtual circuits (PVC) and IP packet flows are configured through this SONET network. ATM switches, or in some cases IP packet switches or routers connect digital subscriber line access multiplexers (DSLAMs) to the SONET network at the network edge and ATM tandem switches or Internet protocol (IP) routers, or class 5 switches, connect to the SONET network at the network core. It has been calculated that installing the facilities and configuring the appropriate circuits currently comprises typically about 29 steps, which will be described later. Each of the different types of network elements (i.e. SONET network nodes, ATM switches, IP routers) requires a different element management system, and the entire network requires at least one network management system, and often a plurality of network management systems. This means that operation support systems (OSSs) providing end-user care functions such as handling new orders, trouble reports, billing, and maintenance functions, must interface to several different types of equipment and several different element, sub-network or even network management systems. Furthermore, the service provider must provide operations personnel in each network node location with such equipment, the personnel being required to be knowledgeable in the various technologies used in different types of nodes used in that location and adjacent locations in the network. Still further, because of the complex configuration of the metropolitan access network, signals must undergo many protocols and physical conversions as they traverse the network. For example, it has been calculated that a signal traveling from end-user A to end-user B in the same metropolitan area goes through a series of typically up to 34 operations, which will be described later, including typically about 12 series optical transmit or receive operations for a distance which is rarely over 80 kilometers.
With regard to the broadband access portion of the metropolitan networks, the most promising proposal to-date is the full services access network (FSAN), which is in ATM-based broadband passive optical network (PON), under joint development and study by a number of telecommunications companies to provide an FTTX solution, in conjunction with VDSL, ADSL or direct fiber in to the end customer. FTTX is an acronym encompassing many types of solutions where “FTT” stands for: fiber-to-the and where X=H(Home), B (Business), C (Curb, with VDSL), Cab (Cabinet, also known as JWI, SAI, and using long-reach VDSL or ADSL), and U (User . . . any of the above). However, as FSAN is to be an open system interconnect (OSI) layer-2 (i.e. ATM-based) network requiring at least one virtual circuit to each end-user, to ensure that the quality of service (QoS) committed to that end-user is maintained, it will still entail significant complexity to operate.
Prior art metropolitan optical networks are costly, difficult-to-deploy, and error-prone. They are also unreliable, complex and power-hungry. Some of the reasons include:                a. Cost                    i. Cost breaks down into capital cost and cost-of-ownership, which includes all aspects of operations cost (equipping, sparing, provisioning, commissioning, data-fills, normal operation (including Network Management operation) trouble shooting, repair, etc.)                        b. Difficult-to-deploy                    i. Multiple, somewhat incompatible systems make up the overall offering. They do not usually have integrated provisioning, maintenance, etc. across the different building blocks, so this has to be provided indirectly by another network management layer            ii. Much of the interconnecting of the initial network set up has to be done manually, and substantial human interaction is required to set up network connections. This results in long set-up times and complex administration systems                        c. Error-prone                    i. Both the initial installation and the setting up of connections in response to customer requirements include complex systems with lots of human interaction, which provides plenty of scope for errors                        d. Unreliable                    i. Network fundamental complexity            ii. Service set up complexity/software complexity            iii. Multiple series functions any one of which can fail            iv. Very hot, dense equipment            v. Non-ideally integrated OAM systems, difficult recovery from some fault conditions                        e. Complex                    i. Non functionally integrated solutions            ii. Many network layers involved, with lots of fine granularity Activities            iii. Complexity of individual functions (electro-optic switch/cross-connect, transponders which are used liberally)                        
Referring to FIGS. 1a, 1b, and 1c, three examples types of prior art metropolitan access networks, each corresponding to a different type of carrier, will be discussed. The most well-established and most conservative are the Incumbent Local Exchange Carriers (ILECs). An example ILEC network 208 is shown in FIG. 1a. The ILECs usually have a high level of presence and infrastructure throughout the Metro area under consideration. The very scale and ubiquity of their plant makes them very cautious and conservative and often they will only move to adopt new things once they are forced to by their more aggressive, agile and nimble competition. The ILEC's networks are optimized upon rights of ways and investments of a past era, for instance being copper twisted pair cable-intensive and with Metro CO's placed at locations dictated by the properties of those cables. It is not uncommon for an ILEC to have 20-50 Central Offices in a large Metro area. The ILEC's have, of course, been upgrading their plant with digital switches and fiber ring transmission, typically still using the old rights of way, and tend to use a two or three tier ring approach to interoffice plant. A three-tier ring, typical of the largest ILEC's and the most major metropolitan areas, is shown in FIG. 1a. 
Referring to FIG. 1a, the example ILEC network 208 connect customer sites 216, possibly interconnected via a ring topology 217, to secondary CO's or metro points-of-presence (POP) 218. The secondary CO's 218 are interconnected via a secondary ring 219 which connects to a core high capacity metro ring 223. The core metro ring 223, consists of 3-5 major (backbone) CO's 221, and has a long haul gateway 220 connecting it to a regional or long haul network 222. These rings are typically implemented at the physical/transport layer using Sonet/SDH rings with Add-Drop Multiplexers providing STS or even VT granularity, along with ATM switches to provide additional layer-2 functionality at key entry, tandem points for data connections or cell-encapsulated voice trunks. Alternatively, for IP packet data only, packet routers may be used in multiple nodes to provide the necessary functionality above layer 1. In particular, the use of routing at intermediate nodes permits dynamic traffic reconfiguration, but at the expense of complex routers, potential traffic degradation due to QoS issues associated with heavy traffic transients on the routers, leading to packet loss, or delay.
In this way fiber connectivity is established to all CO's but up to three series rings have to be traversed in order to achieve a fiber-connected path from any CO to any other in the metro network. In the secondary CO's 218 (those served off of the secondary rings 219) and for local traffic in the fiber center-equipped CO's, the fiber rings 218 feed a plethora of vehicles feeding the access including DSLAM's and DSLAM look-alikes such as Nortel Networks UE9000, DLC's and super DLC's such as Nortel Networks S/DMS AccessNode, point-to-point fiber systems such as Nortel Networks FMT 150, etc. to provide the range of services, capabilities and customer types that are needed to be provided. Due to the tree and branch topology of the ILEC's access rights of way they often cannot extend rings out from the end CO 218 but must use point-to-point vehicles as an extension off of a ring. Hence broadband traffic from one customer premises to another within the same city has to transit 5 fiber systems and four cross-connection points or systems. The ILEC's multiple buildings means that they have the real estate to house any expansion, but only at the cost of maintaining those large (expensive to upkeep) buildings and the equipment within those buildings. However the ILEC does usually own the rights-of-way for the access plant homing into those buildings, even if the ILEC hasn't modernized it/fibered it yet, so can conceptually provide a future seamless user-to-long haul gateway solution better than the competitors.
The flow of traffic for a transport service from customer A to customer B is as follows:
The signals, in their final electrical form (which usually means voice into DS-1's into Sonet VT's and data packets into ATM cells into an ATM PVC into Sonet STS-1, STS-3c or STS-12c) are then multiplexed (if necessary) up to the final optical carrier bit rate/capacity and then modulated into an optical carrier at A, passed up the (in this case point-to-point) access system 216a to the head-end where it is received, turned into an electrical signal at the Sonet/SDH line rate is demultiplexer (if necessary) down to a bit rate acceptable to the cross-connect, cross-connected/inserted (usually at the STS level, though additional ATM switching and/or IP packet routing may be done at this point, to increase the aggregated traffic fill, on the principle of more and more bandwidth utilization efficiency, since bandwidth is so expensive . . . a self-fulfilling proposition, since the implementation is so complex) into the appropriate bandwidth component in the subtending metro core POP 218a, re-modulated (usually using Sonet/SDH) on to an optical carrier for transmission around the collector ring 219 to the next node where it is received, cross-connected electrically and re-modulated on to a (different) optical carrier, by a process of Optical-electrical conversion, electrical switching and electrical-optical conversion. This process is repeated until it reaches a Metro POP hub site 218b on to the core hub ring 223 where again it is received, cross-connected at the Sonet and possibly cell or packet level and impressed on to another Sonet/SDH optical carrier, this time on the core ring 223 between all of the hub sites. It continues step-by-step around the core hub ring 223 until it reaches the appropriate collector ring 219b to feed the local central office feeding B, whereupon it is cross-connected off of the core hub ring 223 on to the subtending collector ring 219b feeding down to the CO 216b at the end of the access ring system feeding B. It transitions each intermediate node between its entry point on the collector ring 219 and the CO 216b feeding B by going through the same reception, electrical cross-connection and re-modulation process as was done on the prior rings until it finally reaches the CO 216b feeding the access ring system 217b out to B. At that CO 216b it is cross-connected electrically into the bit stream going into the access system that feeds through B and then proceeds around the access ring 217b to B, having gone through another round of reception, cross-connection, re-modulation at each intermediate node.
In the example shown above, from customer (Cust) A to B there are the following steps of Optical Tx, (Tx), Optical Rx (Rx) and electrical switching, interconnect or cross-connection (XC) in the Access (Acc), Collector rings (Coll) and Hub rings (Hub), as follows:
TABLE 1Steps involved in transferring a packet from customer A to B1. Cust A Tx10. Coll ring Tx19. XC à Coil ring Tx28. Acc Tx2. AccRx11. Coll Ring Rx20. Coll Ring Rx29. Acc Rx3. Acc/Coll XC12. Coll Ring/Hub21. Coll Ring X-c*30. Acc XCring X-c*4. Coll ring Tx13. Hub ring Tx22. Coll ring Tx31. Acc Tx5. Coll Ring Rx14. Hub Ring Rx23. Coll Ring Rx32. Acc Rx6. Coll Ring X-c*15. Hub Ring X-c*24. Coll Ring X-c*33. Acc/Cust X-c*7. Coll ring Tx16. Hub ring Tx25. Coll ring Tx34. Tx to cust B8. Coll Ring Rx17. Hub Ring Rx26. Coll Ring Rx35. Cust B Rx9. Coll Ring X-c*18. Hub Ring/Coll27. Coll Ring/AccRingring X-c** = Cross-connection is at the Sonet STS level but may also include further traffic cross-connection, switching or routing functions, via an ATM switch or IP router. In particular further packet traffic bandwidth aggregation may occur via tandem routers, resulting in higher data “fills” in the transport pipes. There is a total of 35 concatenated operations including 12 series Optical Tx operations. Yet the distance between customer A and Customer B in the same metro space is rarely more than 80 km, which can be achieved in 1 or 2 optical span reaches. This multiple level of concatenation tends to make for costly, difficult-to-deploy, unreliable, complex, power-hungry and error-prone networks.
FIG. 1b shows an example Mature Competitive Local Exchange Carrier (CLEC) network 204. Mature CLECs were once aggressive new entrants but have become more conservative with time. They are likely to have a major but not ubiquitous presence in a given metro area and have limited fiber, fiber rights-of-way, so may have difficulty reaching whole sub-sections of a given metro area. However they are usually quicker than the ILEC's to apply new technologies and capabilities, but also expect quicker pay-back.
The example CLEC network 204 operates on the same generic principles as those of the ILEC example previously described, and consists of a set of central Metro core Points of Presence 218 connected to a Long Haul or Regional gateway 220 (or Gateways to multiple LH/Regional carriers networks 222). These Points of Presence 218 connect to the outlying Central Offices 216 via fiber (often WDM) rings 217. The outlying CO's 216 then connect into the access by rings, busses and point-to-point systems. For business customers, where two or more routes exist into the business site a ring can be implemented but often, especially for the smaller business and residence, a ring cannot be implemented and point-to-point or add-drop buss structures have to be used.
FIG. 1c shows an example new entrant network 206. The new entrant network 206 (which again operates on the same principles as already described but may be more likely to use the Sonet-IP variant in lieu of the Sonet-ATM variant) has several access rings 217 connected to a metro core POP 224, which provides access to a long haul or regional network 222. The access rings 217 tend to serve large business customers 216 directly. The new entrants tend to use networks that are not as layered as the mature CLEC, and consequently have less complexity to deal with. They new entrants tend to have an abundance of ring-based access because they are servicing large/medium business customers where methods of deploying rings can be found. The new entrants often are formed around bringing a particular new value proposition to market and are often willing to look at novel approaches as long as they perceive that this will give them an unfair advantage, is relevant to their business, can give a fast pay-back and can be handled within the budget and time-scales of such a new entrant.
FIG. 1d shows the network of FIG. 1a with the addition of network managements. Specifically, the following have been added, an access network manager, an IP manager, an ATM manager, a transport network manager, a network manager connected to the other managers with customer service interfaces coupled thereto.
Referring to FIG. 2a, the steps involved for configuring an example prior art metro access network 210 will now be described. The first six steps are to install the network elements (NE) which include, starting from the customer end: a DSLAM 300, an ATM multiplexer 304, at least one level of SONET ring 310 of four add-drop multiplexers (ADMs) 308, which might be repeated several times across any given cross section of a metro network, especially for ILEC's, and a core tandeming and long haul gateway network node, 399, which will act as the service-level demarcation point from metro into long haul and which has therefore to deal with the individual services and circuits at the per-service or per-circuit level. The core tandeming node consists of a SONET digital cross-connect switch (DCS) 314, (which also might also be repeated in other tandeming nodes, between the various layers of rings even if those nodes do not have a long-haul gateway function), an ATM switch 318 (at any point where access is required to the data payload of the Sonet for purposes of service-level manipulation or sub-STS granularity routing), and a core router 322, which provides the packet service routing and aggregation both back into the metro network and into the various long-haul networks, via Sonet interfaces, the Sonet DCS and subtending long-haul trunk Sonet equipment which is not shown but would subtend off of the Sonet DCS. FIG. 2a shows just a simple centralized router here but in practice this would normally be distributed into multiple nodes somewhat similar to the upcoming FIG. 2b, with those routers at the non-gateway nodes just having a role of further data stat. muxing and aggregation to create further network bandwidth utilization efficiencies. Whilst it is apparent that a practical ILEC network can be much more complex than what is described here, by employing several stages of rings, and potentially deploying ATM switches and/or routers in other network nodes, this further increases the complexity and cost of implementing this style of network, so only the relatively simple (but still complex) tasks of setting up the network path of FIG. 2a will be described. The next five steps are to install NE management systems (not shown) for the router 322, the ATM switch 318 and ATM mux 304, the SONET ring 310, the DCS 314, and the DSLAM 300. The next six steps are to install: a DS3 link 302 from the DSLAM 300 to the ATM mux 304, an OC3 fiber 306 from the ATM mux 304 to the SONET ADM 308, a fiber for the SONET ring 310, an OC12 fiber 312 from the SONET ring 310 to the SONET DCS 314, an OC12 fiber 316 from the SONET DCS 413 to the ATM switch 318, and an OC12 fiber 320 from the ATM switch 318 to the core router 322. Next a Sonet transport connection, assumed here to be an STS3c must be configured across the SONET ring 310. Then another STS3c must be configured through the SONET DCS 314. The next six steps are to configure the layer-2 interfaces as follows: DS3 user-to-network interface (UNI) on DSLAM 300, DS3 UNI on ATM Mux 304, OC3 UNI on ATM mux 304, OC3 UNI on ATM switch 318, OC12 UNI on ATM switch 318, OC12 UNI on core router 322. Finally, the last three steps, required to provision a subscriber's ISP connection, are as follows: provision a virtual circuit identifier (VCI) on the DSLAM 300, provision a VCI through the ATM mux 304, and provision a VCI through the ATM switch 318. These last three steps need to be repeated for each subscriber added to the network 210. Whilst this is shown for the case of a single layer of rings, in practice there may be multiple layers, as is shown in FIGS. 1a, 1b, all interconnected with ADM's or DCS's, and both ATM switches and routers may be deployed in intermediate nodes to improve the bandwidth efficiency and traffic handling of the data portion of the network. In addition there are many variations upon the basic theme of the network designs above, as has been indicated. This also extends into using a mesh of STS switches interconnected with point-to-point Sonet links with or without DWDM, to create a mesh instead of ring-based fiber transport layer.
FIG. 2b. shows the same subset path slice through an alternative prior art metropolitan network, but one that is based on IP-packet routers and Sonet STS-level transport traffic provisioning. The Sonet links may be in the form of physical rings, with logical rings used for non-routed traffic and tandem routing of data traffic using the rings as point-to-point Sonet pipes. This results in a very high efficiency flexible network, but at the cost of poor overload/peak traffic behaviour, due to massive QoS fall-off at high loads, due to the packet discards at intermediate nodes, which triggers the TCP layer to re-try transmission, resulting in much of the network traffic being lost and resent, just at the time of peak load when the network cannot tolerate inefficient operation. This is seen by end users as a massive reduction in network performance at peak times. In addition such a network is relatively costly per unit of delivered bandwidth, forcing the extreme use of technique to maximize the bandwidth utilization efficiency in an attempt to achieve a cost-effective way forward. The operation of the network path can be explained in simple steps analogous to those of the supporting text to FIG. 2a, but that description has been omitted here for brevity.
FIG. 2c graphically illustrates the communications layers corresponding to a path through each portion of the network of FIG. 2a-1.
Similarily FIG. 2d graphically illustrates the communications layer corresponding to a path through each portion of the network of FIG. 2b-1.
In both FIGS. 2c and 2d, the DWDM layer is only used for the SONET ring link.
FIG. 2e illustrates the network of FIGS. 2a-1 and 2c with the management layer added.
FIG. 2f illustrates the network of FIGS. 2b-1 and 2d with the management layer added.
FIGS. 2c-2f graphically illustrate the multitude of protocal changes required to traverse the network from access to core.
Typically in prior art MANs, the data switching granularity of the networks tends to increase as data traffic flows towards the core of the network. This prior art approach to data switching leads to a large number of Ethernet/IP data service-aware and service manipulating switches at the edge of the network, perhaps in the local central offices, with a fiber ring structure connecting the service-aware switches together. Such an approach is incompatible with direct photonic connections with minimal hops.
Legacy services, such as telephony, in the metropolitan area network will need to be supported by any new network configurations adopted by a service provider, just as new high bandwidth services, including some not yet envisioned, will also need to be supported. What is desired is a network that is cost-effective to install and operate, and yet is sufficiently flexible and scalable to enable service providers to keep pace with the growth in demand for new services and profitably provide these services to their metropolitan area customers.